Diseases That Cats Can Transmit To Humans

Over the years cats have become the world’s most popular pet owing to their irresistible mysterious charm. Many are even treated as more than pets but as members of the family — sleeping in their human’s beds and sharing a meal at the table. A fair number of felines are also engaged as emotional support cats or therapy cats. This places them in close contact with people which increases the risk of cats transmitting diseases to humans.

Most cats are not considered as pets but as family members and sleep in their human’s beds.

Diseases that may be transmitted between animals and humans are called zoonoses. Only a few of these diseases pose serious health threats in persons who are healthy and have a fully functional immune system. At higher risk for becoming gravely ill are those individuals who are immunocompromised. They are those people suffering from chronic disease, undergoing cancer chemotherapy, have conditions that affect the immune system like Acquired Immunodeficiency Syndrome (AIDS), or taking immunosuppressive drugs like after organ or bone marrow transplant. Also having increased risk are pregnant women, very young children and the elderly.

How Can People Get Zoonotic Diseases From Cats?

There are a number of ways by which people can get zoonotic diseases from cats. Sometimes these different modes of transmission may overlap with each other. Most skin diseases and external parasites are transferred by close and direct physical contact with skin and fur. Some infectious agents are passed through inhaled air.

diseases passed on through bites
Biting passes disease.

The cat’s mouth harbors numerous microorganisms, some of them having the potential to cause disease. Any break on a person’s skin barrier such as wounds inflicted in biting and scratching can serve as a portal for entry for these microbes. Even licking of previously existing wounds or abrasions can transmit these microorganisms.

Another major mode of transfer of infectious agents from cat to man is through vectors. Vector-borne diseases are those infections caused by parasites, viruses, bacteria and other microbes transmitted to man by the bite of infected arthropods. In the case of cats, the most common arthropod vector involved is the flea.

Some cat diseases are feco-orally transmitted. This means that the infectious agents are shed in the feces of infected cats and gain entry into the human’s body through the mouth. This route of transmission may either be direct or indirect. Direct is when feces-contaminated hands touch the mouth. Indirect is through the consumption of contaminated food and water or the use of contaminated utensils. Infected cat feces may also contaminate other household objects, garden soil, sometimes even children’s sandboxes when cats mistake them for litterboxes. Handling of these items then touching the mouth or eating unwashed, raw or undercooked fruits and vegetables may transmit disease.

What Are The Diseases I May Catch From My Cat?

Infectious agents causing zoonotic disease can either be bacteria, viruses, protozoans, fungi, or parasitic worms. Mentioned herein are only the most common zoonoses from each category of infectious agents.

Bacterial Zoonoses

cat fleas
A cat with fleas could be a danger hazard for humans. It is very important to make sure that an infected cat does not bite you or lick any open wounds you may have.

Cat Scratch Disease. This is caused by the bacteria Bartonella henselae found in the saliva of infected cats.  This bacteria is also found in the body of cat fleas and may be transmitted between cats through the bite of these infected fleas. In humans, this bacteria is transmitted through cat bites and licking of scratches or other open wounds. The feces of infected fleas can also be a source of infection if they gain entry to open wounds. In average healthy humans, Cat Scratch Disease symptoms are mild flu-like but they might be severe for those who are immunocompromised.

 

The bacteria Pasteurella multocida are normally present in the mouth of even healthy cats. They can be transmitted to man also through bites, scratches and licking of open wounds. Infection commonly results in a localized skin wound infection. When a person’s immune system is not working properly, the bacteria may go to the bloodstream and cause serious life-threatening infection.

Salmonella bacteria is found in the gastrointestinal tract and is shed in the feces of an infected cat. Cats can get this bacteria from eating raw meat or wild animals it has caught outside. The most common source of Salmonella infection in humans is consumption of food, especially raw or undercooked, that are contaminated with infected cat feces. Cross contamination of utensils and other items with infected material is also a significant mode of transmission. Salmonellosis results to gastrointestinal symptoms in humans like vomiting, diarrhea, stomach ache and dehydration.

One of the more alarming microbes humans can get from infected cats is MRSA. It stands for Methicillin Resistant Staphylococcus aureus. Regular S. aureus is common bacteria found in skin of both cats and humans. MRSA is a strain that is more difficult to treat than other strains of S. aureus because it has developed resistance to the commonly used antibiotics. Cats can carry MRSA without showing symptoms but can still transmit the bacteria to humans through direct contact. In can cause mild skin infection in humans but may become severe. If the bacteria enters the bloodstream it results in life-threatening disease. E

Yersenia pestis is the bacteria that causes the infamous Plague or Black Death. Cats can catch this bacteria from hunting and eating infected rodents or from bites of infected fleas. Infected cats can transmit plague to humans through bites, scratches and contact with respiratory secretions when the cat coughs and sneezes. People can also get infected through bite of infected cat fleas or accidental  swallowing of these fleas. There are three forms of the Plague but the most common one is the Bubonic Plague wherein the lymph nodes will swell. The other more severe forms are Pneumonic Plague when bacteria infects the lungs and Septicemic Plague when the bacteria enters the bloodstream. These three forms may overlap with each other.

Bite from infected cat flea is a major route of transmission of the Plague to humans.

Viral Zoonoses

Fortunately majority of the viruses affecting cats are not zoonotic and cannot cause disease in humans. One virus that is zoonotic is rabies. The usual reservoir of the rabies virus in the wild are the skunks, raccoons, foxes and bats. Cats that come into contact with infected wild or domestic animals are susceptible to getting rabies, especially when there is a biting incident involved. Cats can then transmit the rabies virus to humans through contact with infected saliva through bites and licking of scratches and open wounds. In both cats and humans, the rabies virus attacks the central nervous system.

rabies
You will notice a sudden change in your cats behaviour if it has rabies.

In cats, signs of rabies infection usually start with what is called the “prodromal stage” wherein there is a marked change in the cat’s behavior. The calm cats suddenly become aggressive and the usually active cats suddenly withdraw and hide. This is followed by the “furious stage” wherein the infected cat becomes vicious and will bite or scratch even without provocation. Spasms in the throat muscles make it difficult and painful for the cat to swallow therefore there is the commonly seen sign of excessive drooling of saliva. The third and last stage is called the “paralytic stage” wherein as the name implies, paralysis occurs and the cat can go into a depressed and later a comatose state and die. In all the three stages, the pupil in the cat’s eyes are widely dilated therefore bright lights will make them uncomfortable and they tend to become afraid of light.

In humans, rabies infection can begin to manifest with general malaise and flu-like symptoms. It then progresses to symptoms related to the nervous system like delirium, hallucinations and paralysis. In cats and humans, rabies is fatal when symptoms have started to develop. In bite incidents, if the cat or another animal involved tests positive for rabies or cannot be tested and observed,  start immediately the vaccination with immunoglobulin and active vaccine  in humans.

Parasitic Zoonoses

Fleas are a common ectoparasite found in cats. They can be transferred from cat to cat by contact. Infected fleas can carry tapeworm eggs that can infect cats when swallowed during grooming. They can also occasionally transmit such worms to humans if infected fleas are accidentally swallowed. Flea bites cause intense itching and skin rashes in humans. Fleas are also arthropod vectors of the causative microbes of such diseases as Cat Scratch Fever, Murine Typhus and Plague.

Ticks and mites are less common ectoparasites of cats. Bite of infected ticks can transmit Lyme Disease to humans. Sarcoptes scabei mites causes itchy mange which can be passed to people from close contact with infected cats.

Roundworms can infect cats when the latter eat the meat of infected rodents that have roundworm larvae in their tissues.  Cats can also sometimes swallow the roundworm eggs from being in contact with   feces of infected cats. Some roundworm larvae are passed through the queen’s milk infecting newborn kittens. Roundworms cause mild gastrointestinal-related symptoms in infected cats.  Chronic roundworm infection can cause anemia.

Roundworms suck blood from the intestines causing anemia. High numbers of roundworms can even cause intestinal blockage.

Humans are accidental hosts of roundworms from cats when they unintentionally swallow infective eggs in contaminated soil or eat the intermediate host of the parasite like rabbits. The roundworm eggs hatch in the intestines and then the larvae penetrate the wall and gets carried by the blood to various organs like the heart, lungs, liver, brain, muscle and eyes where they can elicit severe local inflammatory reactions. This is called Toxocariasis or Visceral Larva Migrans. When the eyes are involved, the condition is called Ocular Larva Migrans.

Cats can get hookworm infection when they eat rodents that harbor the parasite’s infective stage in their tissues. Another route of infection is when cats walk on contaminated soil and the hookworm larvae penetrate their skin. Kitten can also get hookworm when they suckle their mother’s infected milk. The hookworms develop in the cat’s intestine and lay eggs there. Large numbers of hookworm in the intestine can cause diarrhea and result in blood loss anemia. The eggs are then passed into the environment together with the cat’s feces. These eggs develop in the soil to become the infective stage larvae.

The infective larvae in the soil can penetrate bare human skin on contact. Humans are at risk for infection when they walk barefoot in contaminated soil. The larva migrates under the skin causing itchiness and irritation. The track the hookworms make when migrating produce linear lesions on the skin. This condition is called Ancylostomiasis or Cutaneous Larva Migrans.

Hookworm larvae migrate under the skin to cause these tracts in Cutaneous Larva Migrans

Another potentially zoonotic parasite of cats is the tapeworm. Cats get infected with tapeworm from eating infected rodents or swallowing infected fleas. Humans get tapeworm by accidentally swallowing tapeworm eggs from eating or drinking contaminated food or water. Handling of other contaminated items and then placing hands in the mouth can also transmit tapeworm eggs to humans. In tapeworm infection, cysts grow slowly in multiple organs in the body and does not cause clinical signs until big enough to interfere with functions of organs.

Fungal Zoonoses

Humans can get Ringworm or Dermatophytosis from direct contact with an infected cat’s skin and fur. Fungal spores also drop from an infected cat’s skin and fur and contaminate the environment which can be a source of infection. Common symptoms of ringworm infection in both cats and humans are scaling like dandruff and itchiness. There are localized round patches of hair loss with a red center which appear like rashes or sometimes blister-like skin lesions. More severe infection in cats result in lesions all over the body. It is, however, also possible for an infected cat to be asymptomatic.

Fungal skin infection in cats seen here on examination under Wood’s lamp ultraviolet light can be transmitted to humans by close physical contact.

Sporotrichosis is another potentially zoonotic fungal disease from cats. It can be acquired from direct contact with an infected cat through cuts on the skin. In humans, sporotrichosis commonly results in a localized skin infection. More severe systemic infection can affect internal organs particularly the lungs.

Protozoal Zoonoses

rodent
Eating rodents that harbor the infective stages of Toxoplasma can transmit the disease to cats.

Toxoplasmosis is one of the most well-known protozoal zoonotic diseases from cats. Cats get infected by eating infected rodents harboring the Toxoplasma cysts in their bodies. Infected cats then shed the parasite spores called oocysts in their feces starting from 2-3 weeks after infection. The oocysts shed in the cat’s feces must first mature in 1-5 days before they are infective to others. Once infective, they are stable in the environment and can continue to be infective for months.

Direct contact between infected cat and humans is not likely to transmit Toxoplasmosis. Humans more commonly get the infection indirectly by coming into contact with infective oocysts in areas where cats and wildlife defecate like litterboxes, garden soil and open sandboxes. Gardening without gloves increases the risk for getting the infection. Humans can also acquire Toxoplasmosis by eating unwashed fruits and vegetables or drinking water than has been contaminated with infective fecal matter. Most human infections are asymptomatic. Symptoms begin as mild flu-like but may progress to severe seizures in immunocompromised persons. Also at risk for severe infection are infants whose mothers were infected while they were pregnant.

Other zoonotic disease caused by protozoans are Giardiasis and Cryptosporidiosis. Cats acquire these single-celled protozoan organisms by coming into contact with and ingesting the infective stages of these parasites. Although humans more frequently get infected with Giardia and Cryptosporidia from other sources, sometimes infection can happen through direct or indirect contact with the feces of infected cats, drinking contaminated water and eating raw or undercooked contaminated food. Humans can suffer from vomiting, diarrhea and dehydration when infected with these protozoal organisms.

 

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